Ignition fault analyser

ABSTRACT

A dynamic spark plug tester adapted for use in testing spark plugs installed on an operating engine. The tester includes a hand actuable clamp alternatively engageable with the high voltage input cable to the distributor associated with such engine or with individual high voltage cables connecting the distributor to respective spark plugs. The clamp incorporates a capacitive coupling element engageable with such cables and has a hand engageable handle portion which carries a compact housing in which test circuitry and an indicating lamp are contained. A ground cable connected to such circuitry is fixedly supported by the handle and terminates remotely from the handle in a ground clip which may be attached to the engine or vehicle frame for completing the tester circuit.

United States Patent [191 [111 3,763,421

Glomski 1 Oct. 2, 1973 IGNITION FAULT ANALYSER [75] Inventor: Arthur F. Glomski, Paw Paw, Mich.

[73 Assignee: Allen Electric and Equipment Company, Kalamazoo, Mich.

[221 Filed: Sept. 9, 1971 [21] Appl. No.: 178,891

Primary Examiner-Michael .I. Lynch Art0rney-Woodhams, Blanchard & Flynn A dynamic spark plug tester adapted for use in testing spark plugs installed on an operating engine. The tester includes a hand actuable clamp alternatively engageable with the high voltage input cable to the distributor associated with such engine or with individual high voltage cables connecting the distributor to respective spark plugs. The clamp incorporates a capacitive coupling element engageable with such cables and has a hand engageable handle portion which carries a compact housing in which test circuitry and an indicating lamp are contained. A ground cable connected to such circuitry is fixedly supported by the handle and terminates remotely from the handle in a ground clip which may be attached to the engine or vehicle frame for completing the tester circuit.

ABSTRACT 11 Claims, 8 Drawing Figures IGNITION FAULT ANALYSER FIELD OF THE INVENTION This invention relates to a spark plug tester and more particularly relates to a compact, self-contained dynamic spark plugtester. 7

BACKGROUND OF THE INVENTION There has been a long-felt need in the automobile maintenance industry for a device for satisfactorily checking proper firing of sprak plugs under actual operating conditions. Previous approaches to this problem have not been fully satisfactory. A common approach used in the past for checking operability of spark plugs on an operating engine has been to remove the spark plugs one at a time from the engine, ground the threaded portion of the sprak plug against the engine block and visually observe whether a spark appears across the plug gap. However, this is unsatisfactory because of the time and energy consumed by maintenance personnel in removing and replacing spark plugs vfrom the block one at a time and because the spark plug being checked is not beingobserved in its normal operating position with its electrodes in the combustion chamber of its associated engine cylinder. More particularly, it is well known that a spark plug which, under atmospheric temperature and pressure conditions may produce a spark, may not when installed in the engine produce a spark or at least a satisfactory spark.

More sophisticated approaches to dynamic testing of spark plugs have generally used test apparatus which is unduly complex and expensive, cumbersome tense and store or incapable of providing a reliable indication of satisfactory spark plug firing.

Accordingly, the objects andpurposes of the present invention include the provision of:

A spark plug tester capable of determining satisfactory firing of spark plugs duringoperation in an associated internal combustion engine.

A spark plug tester, as aforesaid, which in use requires no modification or ,disassembly of the engine being tested or of parts thereof and which is capable of satisfactorily testing spark plugs of internal combustion engines of a wide variety of types under a wide range of operating conditions.

A spark plug tester, as aforesaid, capable of determining that all of the spark plugs of a given engine are operating satisfactorily in a single test operation and alternatively capable of testingindividual ones thereof to determine which individual spark plug has a fault condition.

A spark plug tester, as aforesaid, of simplified construction whichcan be readily and inexpensively manufactured in large or small quantities, which contains a minimal number of parts and which can be stored and shipped in compact packaging.

A spark plug tester, as aforesaid, which requires only two connections to a spark plug ignited engine, in which the sole electrical power requirement is satisfied by such two connections to said engine and in which no external source of power is required for proper operation.

A spark plug tester, as aforesaid, which can be readily used by inexperienced persons with little or no training, which gives a positive indication of satisfac tory spark plug performance under actual engine operating conditions and which is readily and rapidly installable and removable from the engine to be tested.

A spark plug tester, as aforesaid, which is durable and highly reliable in operation over long periods of time under adverse conditions of use and which is constructed in a manner to facilitate rapid repair, including for example rapid replacement of electrical circuitry thereof as a unit.

A spark plug tester, as aforesaid, which is manually clampable to a high tension cable of the engine and establishes a capacitive coupling therewith for picking up signals representative of energy flow to at least one spark plug and which is capable of differentiating between energy flows associated with properly and improperly operating spark plugs.

Other objects and purposes of this invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification andv inspecting the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic side elevational view of an internal combustion engine with a preferred embodiment of the spark plug tester of the present invention in one of its operative positions thereon.

FIG. 2 is an enlarged, partially broken, fragmentary, top elevational view of the spark plug tester of FIG. 1 fixed to a high voltage cable of the engine of FIG. 1.

FIG. 3 is an enlarged side elevational view of the clamp of FIG. 2.

FIG. 4 is a fragmentary, partially broken, enlarged cross-sectional view substantially as taken on the line lV-IV of FIG. 2.

FIG. 5 is a partially broken, cross-sectional view substantially as taken on the line VV of FIG. 4.

FIG. 6 is a schematic diagram of circuitry associated with the preferred embodiment of the invention of FIG. 2.

FIG. 7A is a voltage waveform diagram taken from a portion of FIG. 6 which corresponds to testing of a spark plug which is in satisfactory operative condition.

FIG. 7B is a waveform diagram similar to FIG.'7A but corresponding to testing of a spark plug circuit which is not in proper operative condition and more particularly to a spark plug or supply cable having an open condition.

Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words up, down, right and left will designate directions in the drawings to which reference is made. The words in" and out" will refer to directions toward and away from, respectively, the geometric center of the device and designated parts thereof. Such terminology will include derivatives and words of similar import.

SUMMARY OF THE INVENTION The objects and purposes of the invention are met by providing a dynamic spark plug tester adapted for use in testing spark plugs installed on an operating engine. The tester includes a hand actuable clamp alternatively engageable with the high voltage input cable to the distributor associated with such engine or with individual high voltage cables connecting the distributor to respective spark plugs. The clamp incorporates a capacitive coupling element engageable with such cables and has a hand engageable handle portion which carries a compact housing in which test circuitry and an indicating lamp are contained. A ground cable connected to such circuitry is fixedly supported by the handle and terminates remotely from the handle in a ground clip which may be attached to the engine or vehicle frame.

DETAILED DESCRIPTION FIG. 1 discloses a spark plug tester 10 which is a preferred embodiment of the present invention, installed in one of several alternative positions of use on a spark plug ignited, internal combustion engine 11.

The engine 11 includes a coil 12 which is capable of applying high voltage through an insulated conductor or tower cable 13 to the central input terminal of a distributor 14. The engine 11 includes a plurality of spark plugs 17 which are supplied operating potential by means of insulated conductors, hereinafter referred to as high voltage spark plug cables, 20 from the distributor 14. More particularly, each of the cables connects between a respective spark plug 17 and a respective voltage output terminal on the distributor 14. Thus, the spark plugs 17 are supplied with operating potential sufficient to cause an arc across the electrodes (not shown) thereof in a preselected sequence from the distributor 14 which is in turn supplied with operating potential from the coil 12, all for the purpose of causing the crankshaft 12 of the engine to rotate in a known manner. The engine 11 and its components above described are conventional and are believed to require no further discussion as to structure or operation.

Turning now more particularly to the spark plug tester 10 embodying the present invention, same includes a clamp 24, a circuitry housing 25 and a grounding cable 26 all arranged as a unitary, one-piece test device.

The clamp 24 (FIGS. 2 and 3) comprises a pair of pposed, longitudinally extended legs 28 and 29. In the particular embodiment shown, the legs are of opposed, generally U-shaped cross section, the width of the leg 28 being somewhat greater than the width of the leg 29. An opposed pair of tabs 31 extend downwardly from the side edges of the leg 28 intermediate the ends thereof and snugly but movably overlap corresponding tabs 32 which extend upwardly from the side edges of the lower leg 29 intermediate the ends thereof. The tabs 31 and 32 are preferably located somewhat closer to the rightward ends of the corresponding legs then to the leftward ends thereof. A headed pin or rivet 33 extends transversely of the legs through coaxial openings in the tabs 31 and 32 for pivotally securing the legs 28 and 29 together. The rightward ends of the legs 28 and 29 are preferably urged resiliently toward each other. In the embodiment shown, this is accomplished by a coil spring 35 telescoped over the central portion of the pin 33. The ends of the spring 35 extend tangentially and leftwardly away from the pin 33 to bear upon the opposed inner faces of the leftward portions of the legs 28 and 29 for urging same pivotally apart and thereby urging toward each other the rigthward ends of the legs 28 and 29.

The leftward ends of the legs 28 and 29 together define a handle engageable by the hand of the operator. The leftward end of clamp leg 29 is provided with a transversely opposed pair of bendable flaps for securing the grounding cable 26 thereto.

In the preferred embodiment shown, the rightward ends 36 and 37 of the legs 28 and 29, respectively, are

cylindrical and semicircularly curved about an axis transverse to, and preferably perpendicular to, the length of the legs 28 and 29. Opposed, shell-like pickup elements 39 and 40 are fixed to the opposed faces of the curved ends 36 and 37. The pick-up elements 39 and 40 and legs 28 and 29 are preferably of a substantially rigid, electrically conductive material, preferably an electrically conductive metal. In the particular embodiment shown, the pick-up elements 39 and 40 are of copper sheet fixed by soldering to the leg ends 36 and 37.

The pick-up elements 39 and 40 are preferably of opposed hemicircular, or substantially hemicircular, cross section and in the closed condition of the clamp 24 shown in FIG. 3 are located in close spaced or abutting relation to define clamp jaws having a circular passage therebetween. The pick-up elements 39 and 40 extend, as seen in FIG. 2, transversely beyond the transverse ends of the leg ends 36 and 37 and are preferably smoothly and semicircularly curved along their longitudinal dimension. The pick-up elements 39 and 40 are adapted to be placed, by appropriate manipulation of the clamp legs 28 and 29, on opposite sides of and in gripping relation with one of the spark plug cables 20 or the tower cable 13, the curvature of the pick-up element 39 or 40 corresponding to the average normal curvature of such cables 13 and 20 to facilitate clamping of the pick-up elements 39 and 40 thereon.

The housing 25 (FIGS. 4 and 5) is, in the particular embodiment shown, substantially rectangular in form, comprising spaced, parallel top and bottom walls 42 and 43 connected by upstanding side walls 44 and 45 to define a chamber 46 for receiving electrical components hereinafter discussed. The rightward edges, as seen in FIGS. 4 and 5, of the walls 42-45 are joined by an end wall 47 which closes the rightward end of the chamber 46. The housing 45 may be of any desired material including an insulative plastic material and the above-mentioned walls may be joined to each other to define a rigid unit by any conventional means. The top wall 42 is provided with an opening or window 49 adjacent the walls 46 and 47.

The bottom wall 43 extends leftwardly beyond the walls 43-45 to define a mounting flange 52. In the assembled condition of the tester 10, the mounting flange 52 underlies the leftward portion of the clamp leg 29 and is fixed, thereto preferably removably, by any convenient means here including nut and screw assemblies 54, to support the remainder of the housing 25 in cantilevered relationship to one side of the clamp legs 28 and 29.

The ground cable 26 comprises an outer insulation sheath 58 (FIGS. 2 and 4) which has an inner end portion disposed in the leftward end part of the upwardly opening channel-shaped leg 29 and over which the flaps 56 are snugly folded to secure same to the leftward end of the clamp leg 29. The sheath 58 surrounds an electrical conductor 61. The cable 26 extends outwardly beyond the leg of the clamp leg 29 for any convenient distance, usually a foot or more, and terminates at the leftward end in a clip element, such as the conventional alligator or crocodile clip 60 shown in FIG. 2, to which the central conductor 61 is electrically connected by any conventional means. A flexible insulative shield 62 is telescoped over the leftward end of the cable 26 and clip 60 to electrically insulate the latter. In a similar manner, conventional insulative material in the form of sleeving or a coating may be applied to the leftward or handle portions of the legs 28 and 29 of the clamp 24, such material being omitted from the drawings to clarify the disclosure of the clamp 24.

Turning now to the electrical circuitry, including the components disposed within the housing 25, the latter are shown in their physical arrangement in FIGS. 4 and 5 and schematically in FIG. 6. Such circuitry components include a protective resistor 64 having one lead 65 thereof electrically connected to the clamp 24, and thence to the pick-up elements 39 and 40 thereof, preferably by soldering to the interior face of the leg 29 as indicated at 66 (FIG. 2). The other lead of the resistor 64 is connected to the cathode side of a diode 70, to one lead of a capacitor 71 and to the anode of a discharge lamp, preferably a neon lamp, 72. The remaining leads of the lamp 72 and diode 70 are connected to the remaining lead 73 of the capacitor 71 which extends outwardly of the chamber 46 as seen in FIGS. 4 and 5 and is connected preferably by a soldered splice 77 (FIG. 2) to the conductor 61 of the ground cable 26 inboard of the flaps 56. An insulative sleeve 78 is preferably provided over the spliced ends of the conductor 61 and lead 73 to prevent electrical contact thereof with the clamp 24.

The electrical components 64, 70, 71 and 72 are preferably arranged so that the bodies thereof are in spaced relation with each other and with the interior faces of the walls of the housing 25 and further with the side of the lamp 72 located against the top wall 42 of the housing 25 at the window 49 therein so that such lamp is readily visible from outside the housing 25 and so that ignition of the lamp can be visually noted by the operator. The components 64, 70, 71 and 72 arepreferably assembled in a conventional manner and with such components being arranged, substantially in the relative locations shown in FIG. 5,whereafter same can be placed as a unit within the chamber 46. The components are preferably rigidly held in place within such chamber by then filling the chamber with a hardenable potting compound, preferably an epoxy resin. Such compound may be transparent or translucent. Upon hardening of the compound, the components are fixedly located within the housing 25.

OPERATION Although the operation of the device described above will be understood from the foregoing description by skilled persons, a summary of such operation is now given for convenience.

In use, the leftward portions of the legs 28 and 29 of the clamp 24 are gripped by one hand of the operator and squeezed together against the force of the spring 35 to separate the pick-up elements 39 and 40. Thereafter such pick-up elements may be brought into opposed relationship with one of the cables 13 and 20 and the legs 28 and 29 be released. Thereupon, the spring 35 closes the pick-up elements 39 and 40 into clamping contact with the insulative outer wall of such cable 13 or 20. With the clip 60 attached to a suitable ground connection, such as the nut 79 on the engine block indicated in FIG. 1 and with the engine 11 in operation, the testingsequence may be begun.

To test for proper operation of the spark plugs 17, it is preferred that the sequence of test operation begin with the tester clamped to the tower cable 13. If the test indicates as a result of monitoring the cable 13 that all of the spark plugs 17 are firing properly, no further testing of the individual spark plug cables 20 is required. If on the other hand, testing of the tower cable 13 indicates that one of the spark plugs is malfunctioning, for example, has an open connection therein or in the associated circuitry including the associated spark plug cable 20, the spark plugs 17 and associated cables 20 may be tested thereafter by clamping, in the abovedescribed manner, of the tester 10 to each of the spark plug cables 20 in sequence to determine which of the individual spark plugs is malfunctioning.

When the tester 10 is clamped to any one of the cables l3 and 20, passage of current therethrough to fire an associated one or ones of the spark plugs 17 is capacitively sensed by the pick-up elements 39 and 40 to change the potential thereof with respect to ground, here the engine block 11.

FIG. 7A discloses a voltage waveform of the type that would appear between the pick-up elements 39 and 40 and ground if the spark plug to be energized is operating properly. It will be noted that the waveform comprises a negative going spike 81 of substantial amplitude followed by a diminishing alternating waveform which is primarily negative with only a few, very small positive going spikes 82. With such a voltage waveform applied to the circuit elements 70, 711 and 72, the diode will conduct during the negative going portion of the waveform to shunt same around the discharge lamp 72. Consequently, the lamp 72 will not ignite. The small positive going spikes are of voltage amplitude substantially less than the ignition voltage of the lamp 72 and thus cannot ignite same.

In the particular embodiment shown, the lamp 72 has an ignition voltage of about 75 volts. The negative going spike 81 of waveform diagram 7A is, when measured from one of the cables 13 and 20 to ground approximately 7-12 kilovolts which the dropping resistor 64 and diode 70 drops to a potential less than the 75 volt ignition voltage of the neon lamp. Thus, when the engine ingition system is operating properly, the lamp 72 does not ignite.

When, on the other hand, there is an open condition in a spark plug 17 or in its associated cable 20 or partial open condition therein, and if the tester 10 is attached to such cable 20 (or in addition, when there is an open condition in the distributor contacts or cable 13 when the tester 10 is attached to the cable 13), the voltage waveform applied to the pick-up elements 39 and 40 of the tester 10 is that shown in FIG. 7B, namely, a waveform having both negative going and positive going high amplitude spikes 84 and 85. This series of spikes dimishes in time from an initial high amplitude. Under this condition, a corresponding alternating potential is applied by protective resistor 64 to the elements 70, 71 and 72 of FIG. 6. Again, the diode 70 shunts, around the lamp 72, the negative going portion of the signal. However, in this instance, there still remains across the diode 70 a series of positive going spikes 85 which, though dropped in amplitude from their initial several thousand volt level by the dropping resistor 74 and capacitor 711, still exceed the ignition voltage of the lamp 72, the capacitor 71 and the capacitance of the installed clamp 24 cooperating as parts of a voltage divider. Thus, the lamp 72 ignites in response the positive going spikes 85. Consequently, upon occurrence of a fault condition in the cable and spark plugs being monitored by the tester 10 corresponding to the waveform of FIG. 7B, the lamp 72 will ignite to indicate the presence of such fault condition.

Thus, with the tester 10 secured to the lead 13 of HO. 1, ignition of the lamp 72 indicates that there is a faulty cable or spark plug intervening between the tester 10 and the engine block, that is, there ia a faulty or open condition in the cable 13, distributor contacts or one of the cables and plugs 17. If such occurs, the tester 10 is then applied sequentially to ones of the cables 20 until the lamp is again ignited indicating that the fault condition lies in the particular one of the cables 20 (or in the particular associated one of the plugs 17) to which it is connected. At that point, the suspected plug 17 can be removed from the engine and examined for faults or can be replaced.

Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. ln a spark plug tester, the combination comprising:

clamp means for releasable securement to high voltage cable in circuit with a portion of the high voltage ignition circuitry of a spark plug ignited engine, said clamp means including at least one elongated leg;

ground means connectable to the ground side of said high voltage ignition circuitry and including a ground cable fixed to said clamp means; means defining a test circuit electrically connected to said clamp means and to said ground cable and including indicator means for signaling a fault condition in said high voltage circuit of said engine, including a fault in one of the spark plugs; and

housing means fixed to said leg in offset and transversely extending relation thereto and enclosing said test circuit in fixed relation thereto.

2. The device of claim 1 in which said elongate leg has pick-up means at one end thereof for coupling to a high voltage cable of said engine ignition system and has deformable means adjacent the other end thereof for clamping one end portion of said ground cable in firmly fixed relation to said leg, said ground cable comprising an elongate insulated cable having a clip adja cent the other end thereof for attachment to means grounded with respect to the ground side of the spark plugs of said engine and said ground cable having an exposed electrical conductor extending toward said housing means, said electrical conductor being electrically connected to the clip.

3. The device of claim 1 in which said clamp means includes capacitive pick-up elements for clamping semeans and said discharge lamp and forming, with said capacitive pick-up elements, a voltage divider for stepping down the voltage of said high voltage cable to a level useable with said discharge lamp.

4. The device of claim 3 in which said test circuit further includes a protective resistor directly electrically connected to said clamp means on one side thereof and connected to the cathode of said unidirectional conducting means, to said capacitor and to said discharge lamp on the other side thereof.

5. The device of claim 1 in which said clamp means comprises a further elongate leg, means pivotally connecting said legs intermediate the ends thereof for allowing opening and closing movement of an opposed pair of ends of said legs, an opposed pair of pick-up elements fixed on said leg ends, said pick-up elements each comprising a longitudinally curved elongate shell, the curvature of which corresponds at least approximately to the normal curvature of high voltage cable of said ignition system, said pick-up elements having opposed concave faces sized to firmly grip a high voltage cable of said ignition system to support said clamp means thereon and to electrically couple said clamp means to said high voltage cable to allow sensing of high voltage electrical signals passed by said cable.

6. The device of claim 1 including means located adjacent the opposite ends of said leg for securement recurement to said high voltage cable and said test circuit spectively to such high voltage cable and to said ground cable, said housing means comprising a hollow body having an open end adjacent said clamp means and said ground cable and further having a flange extending beyond the open end of said hollow body, said flange contacting said leg intermediate the ends thereof and being fixed thereto.

7. The device of claim 1 in which said test circuit comprises a plurality of components interconnected with said indicator means and said housing means comprises a light transmissive hardenable mass within which said test circuit components are rigidly located, said indicator means comprising a discharge lamp in said mass adjacent a peripheral face thereof, whereby ignition of said discharge lamp is visible outside said housing means.

8. The device of claim 1 in which said housing means comprises wall means defining a hollow body having a closed end and an open end, said indicator means comprising a lamp, said test circuit including a resistor disposed in said housing means adajcent a portion of the wall means thereof and extending away from said closed end wall, said resistor having a first lead extending outwardly through said open end, said lead being electrically connected to said clamping means, said test circuit further including a capacitor having a first lead connected to the other lead of said resistor and extending substantially in parallelism and in spaced relation with said closed end wall and said lamp, said capacitor having second lead having at least a portion extending away from said closed end wall and along a further wall portion of said housing means in spaced relation to said resistor and out of the open end of said housing means for electrical connection to said ground means, a diode interconnected between said other lead of said resistor and said second lead of said capacitor, said lamp having a pair of leads connected respectively to said other lead of said resistor and said second lead of said capacitor, the portions of the interior of said housing not occupied by said resistor, diode, capacitor and lamp being filled with a light transmissive, hardenable compound for holding said circuitry fixedly in place within said housing means.

9. In a spark plug tester, the combination comprising: clamp means for releasable securement to a cable in circuit with a portion of the high voltage ignition circuitry of a spark plug ignited engine, said clamp means comprising a pair of elongate opposed legs, means pivotally connecting said legs intermediate the ends thereof for allowing opening and closing movement of an opposed pair of ends of said legs, a pair of pick-up elements adapted for movement with said leg ends toward and away from each other, said pick-up elements each comprising a curved elongate shell, the curvature of which corresponds at least approximately to the normal curvature of high voltage cables of said ignition system, said shells being of substantially hemicircular cross section for defining a substantially circular cross section passage extending longitudinally through said opposed pair of pick-up elements, said pick-up elements being sized to firmly grip a high voltage cable of said ignition system to support said clamp means threon and to electrically couple said clamp means to said cable to allow sensing of high voltage electrical signals passed by said cable; ground means connected to the ground side of said high voltage ignition circuitry and carried by said clamp means; means defining a test circuit electrically connected to said clamp means and to said ground means and including indicator means for signaling a fault condition in said high voltage circuit of said engine, including a fault in one of the spark plugs; and housing means fixed with respect to said clamp means for carrying said circuitry in fixed relation to said clamp means. 10. In a spark plug tester, the combination comprismg:

clamp means for releasable securement to a cable in circuit with a portion of the high voltage ignition circuitry of a spark plug ignited'engine; ground means connected to the ground side of said high voltage ignition circuitry and carried by said clamp means; means defining a test circuit electrically connected to said clamp means and to said ground means and including indicator means for signaling a fault condition in said high voltage circuit of said engine, including a fault in one of the spark plugs; and

housing means fixed with respect to said clamp means for carrying said circuitry in fixed relation to said clamp means;

said clamp means including at least one elongate leg and means located adjacent the opposite ends of said leg for securement respectively to a cable of said high voltage portion of said ignition system and to said ground means, said housing means comprising wall means defining a hollow body and closing one end of said body leaving the other end of said body open, said wall means including a flange extending beyond the open end of said housing means, said flange underlying said leg intermediate the ends thereof and including means for fixedly connecting said flange to said leg for supporting said housing means in offset and transversely extending relation to said leg.

11. The device of claim 10 in which said housing comprises means defining an opening in a portion of the wall means of said housing means adjacent said closed end thereof, said indicator means comprises a discharge lamp in said housing means adjacent said opening, whereby ignition of said discharge lamp is visible through said opening outside said housing means, said test circuit includes a resistor disposed in said housing means adjacent a portion of the wall means thereof and extending away from said closed end wall, said resistor having a first lead extending outwardly of said housing means in spaced relation to said flange, said lead being electrically connected to said clamping means, said test circuit further including a capacitor having a first lead connected to the other lead of said resistor and extending substantially in parallelism and in spaced relation with said end wall and said lamp, said capacitor having second lead having at least a portion extending away from said closed end wall and along a further wall portion of said housing means in spaced relation to said resistor and out of the open end of said housing means above said flange for electrical connection to said ground means, a diode interconnected between said other lead of said resistor and said second lead of said capacitor, said lamp having a pair of leads connected respectively to said other lead of said resistor and said second lead of said capacitor, the portions of the interior of said housing not occupied by said resistor, diode, capacitor and lamp being filled with a light transmissive, hardenable compound for holding said circuitry fixedly in place within said housing means.

UNITED STATES TATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 763 421 Dated October 2, 1973 lnv n fl Arthur F. Glomski It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 44, change "system to --circuitry-. line 63, change "system" to ignition circuitry--. Column 8, line 20 change "system to c-ircuitry. line 22, change "system" line 66, after "housing" insert --means. Column 9, line 17,

delete "sys-" and insert circuitry" line 18, delete "tem" line 23, delete "system." and insert circuitry.; line 33,

delete "circuit" and insert --circuitry--.; line 36, change "circuitry" to test circuit-. Column 10', line 2, change "circuitry" .to test circuit.; line 7, delete "portion of said"; also change "system" to circuitry.; line 18, after "housing" insert \-means--@ line 27, delete "wall". line 34, before "end" insert --closed--.; also delete "wall".; line 35, after "having" insert --a. line 36 delete "wall".; line 45, after "housing" insert --means--.; line 48, delete "circuitry" and insert test circuit-.

Signed and sealed this 23rd day of April 1971 (SEAL) Attest:

EDWARD l I.'ELETCHER,JR. G. MARSHALL DANN Attesting Officer C Commissioner of Patents I FORM P0405, uscoMM-Dc 60376-P69 v.5. GOVERNMENT FRlNTING OFFICE 1 I98 0-366-334- to circuitry.; line 46, after "closed end" insert wall-- 

1. In a spark plug tester, the combination comprising: clamp means for releasable securement to high voltage cable in circuit with a portion of the high voltage ignition circuitry of a spark plug ignited engine, said clamp means including at least one elongated leg; ground means connectable to the ground side of said high voltage ignition circuitry and including a ground cable fixed to said clamp means; means defining a test circuit electrically connected to said clamp means and to said ground cable and including indicator means for signaling a fault condition in said high voltage circuit of said engine, including a fault in one of the spark plugs; and housing means fixed to said leg in offset and transversely extending relation thereto and enclosing said test circuit in fixed relation thereto.
 2. The device of claim 1 in which said elongate leg has pick-up means at one end thereof for coupling to a high voltage cable of said engine ignition system and has deformable means adjacent the other end thereof for clamping one end portion of said ground cable in firmly fixed relation to said leg, said ground cable comprising an elongaTe insulated cable having a clip adjacent the other end thereof for attachment to means grounded with respect to the ground side of the spark plugs of said engine and said ground cable having an exposed electrical conductor extending toward said housing means, said electrical conductor being electrically connected to the clip.
 3. The device of claim 1 in which said clamp means includes capacitive pick-up elements for clamping securement to said high voltage cable and said test circuit comprises unidirectional conducting means connected between said clamp means and said ground means for conducting in response to a voltage drop between said clamp means and ground means in one direction, a voltage drop in the opposite direction corresponding to a fault condition in said high voltage system, a discharge lamp connected across said unidirectional conducting means for ignition upon a voltage drop thereacross in said opposite direction, a capacitor connected in parallel with each of said unidirectional conducting means and said discharge lamp and forming, with said capacitive pick-up elements, a voltage divider for stepping down the voltage of said high voltage cable to a level useable with said discharge lamp.
 4. The device of claim 3 in which said test circuit further includes a protective resistor directly electrically connected to said clamp means on one side thereof and connected to the cathode of said unidirectional conducting means, to said capacitor and to said discharge lamp on the other side thereof.
 5. The device of claim 1 in which said clamp means comprises a further elongate leg, means pivotally connecting said legs intermediate the ends thereof for allowing opening and closing movement of an opposed pair of ends of said legs, an opposed pair of pick-up elements fixed on said leg ends, said pick-up elements each comprising a longitudinally curved elongate shell, the curvature of which corresponds at least approximately to the normal curvature of high voltage cable of said ignition system, said pick-up elements having opposed concave faces sized to firmly grip a high voltage cable of said ignition system to support said clamp means thereon and to electrically couple said clamp means to said high voltage cable to allow sensing of high voltage electrical signals passed by said cable.
 6. The device of claim 1 including means located adjacent the opposite ends of said leg for securement respectively to such high voltage cable and to said ground cable, said housing means comprising a hollow body having an open end adjacent said clamp means and said ground cable and further having a flange extending beyond the open end of said hollow body, said flange contacting said leg intermediate the ends thereof and being fixed thereto.
 7. The device of claim 1 in which said test circuit comprises a plurality of components interconnected with said indicator means and said housing means comprises a light transmissive hardenable mass within which said test circuit components are rigidly located, said indicator means comprising a discharge lamp in said mass adjacent a peripheral face thereof, whereby ignition of said discharge lamp is visible outside said housing means.
 8. The device of claim 1 in which said housing means comprises wall means defining a hollow body having a closed end and an open end, said indicator means comprising a lamp, said test circuit including a resistor disposed in said housing means adajcent a portion of the wall means thereof and extending away from said closed end wall, said resistor having a first lead extending outwardly through said open end, said lead being electrically connected to said clamping means, said test circuit further including a capacitor having a first lead connected to the other lead of said resistor and extending substantially in parallelism and in spaced relation with said closed end wall and said lamp, said capacitor having second lead having at least a portion extending away from said closed end wall and along a furTher wall portion of said housing means in spaced relation to said resistor and out of the open end of said housing means for electrical connection to said ground means, a diode interconnected between said other lead of said resistor and said second lead of said capacitor, said lamp having a pair of leads connected respectively to said other lead of said resistor and said second lead of said capacitor, the portions of the interior of said housing not occupied by said resistor, diode, capacitor and lamp being filled with a light transmissive, hardenable compound for holding said circuitry fixedly in place within said housing means.
 9. In a spark plug tester, the combination comprising: clamp means for releasable securement to a cable in circuit with a portion of the high voltage ignition circuitry of a spark plug ignited engine, said clamp means comprising a pair of elongate opposed legs, means pivotally connecting said legs intermediate the ends thereof for allowing opening and closing movement of an opposed pair of ends of said legs, a pair of pick-up elements adapted for movement with said leg ends toward and away from each other, said pick-up elements each comprising a curved elongate shell, the curvature of which corresponds at least approximately to the normal curvature of high voltage cables of said ignition system, said shells being of substantially hemicircular cross section for defining a substantially circular cross section passage extending longitudinally through said opposed pair of pick-up elements, said pick-up elements being sized to firmly grip a high voltage cable of said ignition system to support said clamp means threon and to electrically couple said clamp means to said cable to allow sensing of high voltage electrical signals passed by said cable; ground means connected to the ground side of said high voltage ignition circuitry and carried by said clamp means; means defining a test circuit electrically connected to said clamp means and to said ground means and including indicator means for signaling a fault condition in said high voltage circuit of said engine, including a fault in one of the spark plugs; and housing means fixed with respect to said clamp means for carrying said circuitry in fixed relation to said clamp means.
 10. In a spark plug tester, the combination comprising: clamp means for releasable securement to a cable in circuit with a portion of the high voltage ignition circuitry of a spark plug ignited engine; ground means connected to the ground side of said high voltage ignition circuitry and carried by said clamp means; means defining a test circuit electrically connected to said clamp means and to said ground means and including indicator means for signaling a fault condition in said high voltage circuit of said engine, including a fault in one of the spark plugs; and housing means fixed with respect to said clamp means for carrying said circuitry in fixed relation to said clamp means; said clamp means including at least one elongate leg and means located adjacent the opposite ends of said leg for securement respectively to a cable of said high voltage portion of said ignition system and to said ground means, said housing means comprising wall means defining a hollow body and closing one end of said body leaving the other end of said body open, said wall means including a flange extending beyond the open end of said housing means, said flange underlying said leg intermediate the ends thereof and including means for fixedly connecting said flange to said leg for supporting said housing means in offset and transversely extending relation to said leg.
 11. The device of claim 10 in which said housing comprises means defining an opening in a portion of the wall means of said housing means adjacent said closed end thereof, said indicator means comprises a discharge lamp in said housing means adjacent said opening, whereby ignition of said discharge lamp is visible through said openIng outside said housing means, said test circuit includes a resistor disposed in said housing means adjacent a portion of the wall means thereof and extending away from said closed end wall, said resistor having a first lead extending outwardly of said housing means in spaced relation to said flange, said lead being electrically connected to said clamping means, said test circuit further including a capacitor having a first lead connected to the other lead of said resistor and extending substantially in parallelism and in spaced relation with said end wall and said lamp, said capacitor having second lead having at least a portion extending away from said closed end wall and along a further wall portion of said housing means in spaced relation to said resistor and out of the open end of said housing means above said flange for electrical connection to said ground means, a diode interconnected between said other lead of said resistor and said second lead of said capacitor, said lamp having a pair of leads connected respectively to said other lead of said resistor and said second lead of said capacitor, the portions of the interior of said housing not occupied by said resistor, diode, capacitor and lamp being filled with a light transmissive, hardenable compound for holding said circuitry fixedly in place within said housing means. 